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A mitochondrial-focused genetic interaction map reveals a scaffold-like complex required for inner membrane organization in mitochondria.

Hoppins S, Collins SR, Cassidy-Stone A, Hummel E, Devay RM, Lackner LL, Westermann B, Schuldiner M, Weissman JS, Nunnari J - J. Cell Biol. (2011)

Bottom Line: The MITO-MAP also reveals a large inner membrane-associated complex, which we term MitOS for mitochondrial organizing structure, comprised of Fcj1/Mitofilin, a conserved inner membrane protein, and five additional components.We show that MitOS acts in concert with ATP synthase dimers to organize the inner membrane and promote normal mitochondrial morphology.We propose that MitOS acts as a conserved mitochondrial skeletal structure that differentiates regions of the inner membrane to establish the normal internal architecture of mitochondria.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.

ABSTRACT
To broadly explore mitochondrial structure and function as well as the communication of mitochondria with other cellular pathways, we constructed a quantitative, high-density genetic interaction map (the MITO-MAP) in Saccharomyces cerevisiae. The MITO-MAP provides a comprehensive view of mitochondrial function including insights into the activity of uncharacterized mitochondrial proteins and the functional connection between mitochondria and the ER. The MITO-MAP also reveals a large inner membrane-associated complex, which we term MitOS for mitochondrial organizing structure, comprised of Fcj1/Mitofilin, a conserved inner membrane protein, and five additional components. MitOS physically and functionally interacts with both outer and inner membrane components and localizes to extended structures that wrap around the inner membrane. We show that MitOS acts in concert with ATP synthase dimers to organize the inner membrane and promote normal mitochondrial morphology. We propose that MitOS acts as a conserved mitochondrial skeletal structure that differentiates regions of the inner membrane to establish the normal internal architecture of mitochondria.

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MitOS is required for mitochondrial structure. (A) Wild-type and indicated deletion strains expressing matrix-targeted GFP were grown in SD-dextrose and visualized by fluorescent light microscopy. Representative images of each strain are shown. The graph represents quantification of the mitochondrial morphology in the indicated strains. Data are represented as the mean ± standard error (error bars) of three independent experiments characterizing the mitochondrial morphology of ≥75 cells in each replicate. (B) Wild-type and mutant cells were analyzed by thin-section electron microscopy, and representative images of mitochondria are shown. (C) Representative images of cristae junctions (arrows) observed in wild-type and Δfcj1 cells are shown. (D) Quantification of the widths of cristae junctions observed in electron tomograms of wild-type, Δaim5, and Δaim37 cells. Data are represented as the mean ± standard deviation of three independent measurements. Bars: (A) 2 µm; (B) 200 nm; (C) 20 nm.
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fig5: MitOS is required for mitochondrial structure. (A) Wild-type and indicated deletion strains expressing matrix-targeted GFP were grown in SD-dextrose and visualized by fluorescent light microscopy. Representative images of each strain are shown. The graph represents quantification of the mitochondrial morphology in the indicated strains. Data are represented as the mean ± standard error (error bars) of three independent experiments characterizing the mitochondrial morphology of ≥75 cells in each replicate. (B) Wild-type and mutant cells were analyzed by thin-section electron microscopy, and representative images of mitochondria are shown. (C) Representative images of cristae junctions (arrows) observed in wild-type and Δfcj1 cells are shown. (D) Quantification of the widths of cristae junctions observed in electron tomograms of wild-type, Δaim5, and Δaim37 cells. Data are represented as the mean ± standard deviation of three independent measurements. Bars: (A) 2 µm; (B) 200 nm; (C) 20 nm.

Mentions: To determine if MitOS components function in the Fcj1 pathway of mitochondrial inner membrane structure, we assessed mitochondrial morphology and inner membrane structure in MitOS deletion strains by fluorescent light and thin section EM, respectively (Fig. 5, A and B). We observed a similar defect in mitochondrial morphology in each MitOS deletion strain, as assessed by mitochondrial matrix–targeted GFP (mito-GFP). Specifically, aberrant mitochondrial structures composed of large, lamellar sheets were observed in MitOS deletion strains, which were similar in morphology to that described previously for ATP synthase dimerization mutants (Fig. 5 A, representative images shown). Mitochondrial inner membrane structure was also dramatically altered in MitOS deletion cells, with an observed increase in inner membrane cristae length and increase in cristae stacking and wrapping (Fig. 5 B). Furthermore, we frequently observed highly elongated and thinner mitochondria in MitOS deletion cells (e.g., Δaim37 and Δaim13 in Fig. 5 B), which likely correspond to the large, lamellar sheet regions of mitochondria observed by fluorescence microscopy (compare to Fig. 5 A). We observed less severe mitochondrial morphology defects for Δaim5 and Δmos2 cells, and a significantly less severe cristae phenotype in Δmos2, which suggests that Aim5 and Mos2 may possess a more peripheral and/or redundant role within MitOS. This observation is consistent with biochemical data indicating that the steady-state levels of Aim5 and Mos2 are independent of other MitOS subunits (Fig. 3 B). The similarity of the mitochondrial morphology phenotype among MitOS deletion strains indicates that the components of MitOS function in the same pathway to control mitochondrial structure, in agreement with the similarity of their genetic interaction profiles in the MITO-MAP.


A mitochondrial-focused genetic interaction map reveals a scaffold-like complex required for inner membrane organization in mitochondria.

Hoppins S, Collins SR, Cassidy-Stone A, Hummel E, Devay RM, Lackner LL, Westermann B, Schuldiner M, Weissman JS, Nunnari J - J. Cell Biol. (2011)

MitOS is required for mitochondrial structure. (A) Wild-type and indicated deletion strains expressing matrix-targeted GFP were grown in SD-dextrose and visualized by fluorescent light microscopy. Representative images of each strain are shown. The graph represents quantification of the mitochondrial morphology in the indicated strains. Data are represented as the mean ± standard error (error bars) of three independent experiments characterizing the mitochondrial morphology of ≥75 cells in each replicate. (B) Wild-type and mutant cells were analyzed by thin-section electron microscopy, and representative images of mitochondria are shown. (C) Representative images of cristae junctions (arrows) observed in wild-type and Δfcj1 cells are shown. (D) Quantification of the widths of cristae junctions observed in electron tomograms of wild-type, Δaim5, and Δaim37 cells. Data are represented as the mean ± standard deviation of three independent measurements. Bars: (A) 2 µm; (B) 200 nm; (C) 20 nm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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fig5: MitOS is required for mitochondrial structure. (A) Wild-type and indicated deletion strains expressing matrix-targeted GFP were grown in SD-dextrose and visualized by fluorescent light microscopy. Representative images of each strain are shown. The graph represents quantification of the mitochondrial morphology in the indicated strains. Data are represented as the mean ± standard error (error bars) of three independent experiments characterizing the mitochondrial morphology of ≥75 cells in each replicate. (B) Wild-type and mutant cells were analyzed by thin-section electron microscopy, and representative images of mitochondria are shown. (C) Representative images of cristae junctions (arrows) observed in wild-type and Δfcj1 cells are shown. (D) Quantification of the widths of cristae junctions observed in electron tomograms of wild-type, Δaim5, and Δaim37 cells. Data are represented as the mean ± standard deviation of three independent measurements. Bars: (A) 2 µm; (B) 200 nm; (C) 20 nm.
Mentions: To determine if MitOS components function in the Fcj1 pathway of mitochondrial inner membrane structure, we assessed mitochondrial morphology and inner membrane structure in MitOS deletion strains by fluorescent light and thin section EM, respectively (Fig. 5, A and B). We observed a similar defect in mitochondrial morphology in each MitOS deletion strain, as assessed by mitochondrial matrix–targeted GFP (mito-GFP). Specifically, aberrant mitochondrial structures composed of large, lamellar sheets were observed in MitOS deletion strains, which were similar in morphology to that described previously for ATP synthase dimerization mutants (Fig. 5 A, representative images shown). Mitochondrial inner membrane structure was also dramatically altered in MitOS deletion cells, with an observed increase in inner membrane cristae length and increase in cristae stacking and wrapping (Fig. 5 B). Furthermore, we frequently observed highly elongated and thinner mitochondria in MitOS deletion cells (e.g., Δaim37 and Δaim13 in Fig. 5 B), which likely correspond to the large, lamellar sheet regions of mitochondria observed by fluorescence microscopy (compare to Fig. 5 A). We observed less severe mitochondrial morphology defects for Δaim5 and Δmos2 cells, and a significantly less severe cristae phenotype in Δmos2, which suggests that Aim5 and Mos2 may possess a more peripheral and/or redundant role within MitOS. This observation is consistent with biochemical data indicating that the steady-state levels of Aim5 and Mos2 are independent of other MitOS subunits (Fig. 3 B). The similarity of the mitochondrial morphology phenotype among MitOS deletion strains indicates that the components of MitOS function in the same pathway to control mitochondrial structure, in agreement with the similarity of their genetic interaction profiles in the MITO-MAP.

Bottom Line: The MITO-MAP also reveals a large inner membrane-associated complex, which we term MitOS for mitochondrial organizing structure, comprised of Fcj1/Mitofilin, a conserved inner membrane protein, and five additional components.We show that MitOS acts in concert with ATP synthase dimers to organize the inner membrane and promote normal mitochondrial morphology.We propose that MitOS acts as a conserved mitochondrial skeletal structure that differentiates regions of the inner membrane to establish the normal internal architecture of mitochondria.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA.

ABSTRACT
To broadly explore mitochondrial structure and function as well as the communication of mitochondria with other cellular pathways, we constructed a quantitative, high-density genetic interaction map (the MITO-MAP) in Saccharomyces cerevisiae. The MITO-MAP provides a comprehensive view of mitochondrial function including insights into the activity of uncharacterized mitochondrial proteins and the functional connection between mitochondria and the ER. The MITO-MAP also reveals a large inner membrane-associated complex, which we term MitOS for mitochondrial organizing structure, comprised of Fcj1/Mitofilin, a conserved inner membrane protein, and five additional components. MitOS physically and functionally interacts with both outer and inner membrane components and localizes to extended structures that wrap around the inner membrane. We show that MitOS acts in concert with ATP synthase dimers to organize the inner membrane and promote normal mitochondrial morphology. We propose that MitOS acts as a conserved mitochondrial skeletal structure that differentiates regions of the inner membrane to establish the normal internal architecture of mitochondria.

Show MeSH
Related in: MedlinePlus